The present invention relates to coal desulfurization and, more particularly, to efficient and cost-effective means for removing both organic and inorganic sulfur compounds from coal.
A particular atmospheric pollutant of environmental concern is sulfur dioxide (SO.sub.2) produced during the burning of sulfur-containing coal, and it is accordingly a desirable goal to minimize the generation of sulfur dioxide. There are two general approaches which may be employed: the use of low-sulfur coal as fuel, and removal of the sulfur dioxide from the flue gas subsequent to combustion.
There is a relative abundance of high-sulfur coal, making effective sulfur removal processes and equipment quite attractive. Previous approaches, as mentioned briefly above, have been largely directed to removal of sulfur dioxide from combustion products. This is, however, inherently difficult because sulfur dioxide is a gas, in contrast to a particulate, which is somewhat easier to remove through filtering processes, particularly electrostatic filtering.
As an alternative, various processes have been proposed for removal of sulfur from the coal prior to combustion. One known process for removing inorganic sulfur compounds from coal is known as the Meyer process, and is based on the reaction of sulfur-bearing coal with Fe.sub.2 (SO.sub.4).sub.3. Another known coal desulfurization process is the NaOH-Air fusion process, which depends upon the formation of peroxide and OH radicals.
Particularly pertinent in the context of the present invention is one of the processes disclosed in Zenty U.S. Pat. No. 4,177,120, which discloses the desulfurizing of coal by solar radiation in a suitable gaseous environment, specifically, in the absence of molecular oxygen and in the presence of CO.sub.2. In particular, the process which Zenty proposes apparently proceeds according to the following chemical reaction: EQU Sulfur-containing Coal+CO.sub.2 +Energy.fwdarw. Pure Coal+CO+CO.sub.2 +SO.sub.x +NO.sub.x.
Also worthy of some note in the context of the present invention is the disclosure of Inoue U.S. Pat. No. 3,616,375, which proposes the desulfurization of liquid and gaseous organic compounds such as petroleum by imparting energy to the sulfur species directly, via physical means, such as: (1) impulsive electric discharge, (2) sonic vibrations, (3) laser, (4) microwave energy, or (5) high frequency electrostatic field. Based on our analysis, the success of the Inoue process depends upon the ability to transfer appropriate amounts of energy directly to the sulfur species, aided considerably by the nature of the liquid and gaseous hydrocarbons employed, wherein all the constituent molecules are in constant motion and essentially uniformly distributed. This randomness of distribution apparently enhances the likelihood of transferring energy directly to the sulfur-bearing molecule.
Also relevant in the context of the present invention is the invention comprising the subject matter of commonly-assigned application Ser. No. 226,853, filed Jan. 21, 1981, U.S. Pat. No. 4,372,832 by John R. Bush, entitled "Pollution Control by Spray Dryer and Electron Beam Treatment". Bush discloses a particular combination of spray drying and electron beam treatment for effluent gasses for converting gaseous sulfur oxides and nitrogen oxides into mist and/or solid particles, which may then be subjected to dry particulate collection.
By the present invention there are provided electron beam processes and apparatus for desulfurizing coal prior to combustion.